Rain light. Or tornado sky. This acts as a hypnotic on the sympathetic nervous system. Pus. A green room eases the change from one state to another. Mold. As a child, Tolstoy believed that a green stick buried in a ravine near his family's home had the secret of happiness scratched on it. Now his bones lie near that ravine. But you? In color Doppler echocardiographs, fast-moving blood glows green. When you stand among trees and close your eyes, it's easy to imagine you hear an engine running. Usually there is one.